Question 1

A cyclotron operates with a given magnetic field and at a given frequency.If R denotes the radius of the final orbit, the final particle energy is proportional to:

Accepted Answer

A) 1/R 
B) R 
C) R2 
D) R3 
E) R4 
A) 1/R 
B) R 
C) R2 
D) R3 
E) R4

Question 2

The Hall effect can be used to calculate the charge-carrier number density in a conductor.If a conductor carrying a current of 2.0 A is 0.5 mm thick, and the Hall effect voltage is 4.5 µV when it is in a uniform magnetic field of 1.2 T, what is the density of charge carriers in the conductor?

Accepted Answer

A) 1.0 x 1028/m3  
B) 6.7 x 1027/m3 
C) 4.6 x 1027/m3 
D) 1.7 x 1027/m3 
E) 1.2 x 1027/m3 
A) 1.0 x 1028/m3  
B) 6.7 x 1027/m3 
C) 4.6 x 1027/m3 
D) 1.7 x 1027/m3 
E) 1.2 x 1027/m3

Question 3

The diagram shows a straight wire carrying a flow of electrons into the page.The wire is between the poles of a permanent magnet.The direction of the magnetic force exerted on the wire is:

Accepted Answer

A) "$\uparrow$" 
B) "$\downarrow$" 
C) "$\leftarrow$" 
D) "$\rightarrow$" 
E) "into the page" 
A) "$\uparrow$" 
B) "$\downarrow$" 
C) "$\leftarrow$" 
D) "$\rightarrow$" 
E) "into the page"

Question 4

J.J.Thomson's experiment, involving the motion of an electron beam in mutually perpendicular and fields, gave the value of:

Accepted Answer

A) the mass of an electron 
B) the charge of an electron 
C) the Earth's magnetic field 
D) the charge/mass ratio for an electron 
E) Avogadro's number 
A) the mass of an electron 
B) the charge of an electron 
C) the Earth's magnetic field 
D) the charge/mass ratio for an electron 
E) Avogadro's number

Question 5

The figure shows the motion of electrons in a wire which is near the N pole of a magnet.The wire will be pushed:

Accepted Answer

A) toward the magnet 
B) away from the magnet 
C) downward 
D) upward 
E) along its length 
A) toward the magnet 
B) away from the magnet 
C) downward 
D) upward 
E) along its length

Question 6

In the formula F ⃗=qv ⃗×B ⃗ :

Accepted Answer

A)  F ⃗ must be perpendicular to v ⃗  but not necessarily to B ⃗ 
B)  F ⃗ must be perpendicular to B ⃗ but not necessarily to v ⃗ 
C)  v ⃗ must be perpendicular to B ⃗ but not necessarily to F ⃗ 
D) all three vectors must be mutually perpendicular 
E)  F ⃗ must be perpendicular to both v ⃗ and B ⃗ 
A)  F ⃗ must be perpendicular to v ⃗  but not necessarily to B ⃗ 
B)  F ⃗ must be perpendicular to B ⃗ but not necessarily to v ⃗ 
C)  v ⃗ must be perpendicular to B ⃗ but not necessarily to F ⃗ 
D) all three vectors must be mutually perpendicular 
E)  F ⃗ must be perpendicular to both v ⃗ and B ⃗

Question 7

A square loop of wire lies in the plane of the page and carries a current I as shown.There is a uniform magnetic field directed towards the top of the page, as indicated.The loop will tend to rotate:

Accepted Answer

A) about PQ with KL coming out of the page 
B) about PQ with KL going into the page 
C) about RS with MK coming out of the page 
D) about RS with MK going into the page 
E) about an axis perpendicular to the page 
A) about PQ with KL coming out of the page 
B) about PQ with KL going into the page 
C) about RS with MK coming out of the page 
D) about RS with MK going into the page 
E) about an axis perpendicular to the page

Question 8

An electron travels due north through a vacuum in a region of uniform magnetic field that is also directed due north.It will:

Accepted Answer

A) be unaffected by the field 
B) speed up 
C) slow down 
D) follow a right-handed corkscrew path 
E) follow a left-handed corkscrew path 
A) be unaffected by the field 
B) speed up 
C) slow down 
D) follow a right-handed corkscrew path 
E) follow a left-handed corkscrew path

Question 9

The diagram shows a straight wire carrying current i in a uniform magnetic field.The magnetic force on the wire is indicated by an arrow but the magnetic field is not shown.Of the following possibilities, the direction of the magnetic field is:

Accepted Answer

A) to the right 
B) opposite the direction of 
C) in the direction of 
D) into the page 
E) out of the page 
A) to the right 
B) opposite the direction of 
C) in the direction of 
D) into the page 
E) out of the page

Question 10

At any point the magnetic field lines are in the direction of:

Accepted Answer

A) the magnetic force on a moving positive charge 
B) the magnetic force on a moving negative charge 
C) the velocity of a moving positive charge 
D) the velocity of a moving negative charge 
E) none of the above 
A) the magnetic force on a moving positive charge 
B) the magnetic force on a moving negative charge 
C) the velocity of a moving positive charge 
D) the velocity of a moving negative charge 
E) none of the above

Question 11

A uniform magnetic field is directed into the page.A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown.A reasonable explanation is:

Accepted Answer

A) the charge is positive and slowing down 
B) the charge is negative and slowing down 
C) the charge is positive and speeding up 
D) the charge is negative and speeding up 
E) none of the above 
A) the charge is positive and slowing down 
B) the charge is negative and slowing down 
C) the charge is positive and speeding up 
D) the charge is negative and speeding up 
E) none of the above

Question 12

A uniform magnetic field is in the positive z direction.A positively charged particle is moving in the positive x direction through the field.The net force on the particle can be made zero by applying an electric field in what direction?

Accepted Answer

A) Positive y 
B) Negative y 
C) Positive x 
D) Negative x 
E) Positive z 
A) Positive y 
B) Negative y 
C) Positive x 
D) Negative x 
E) Positive z

Question 13

An electron and a proton are both initially moving with the same speed and in the same direction at 90˚ to the same uniform magnetic field.They experience magnetic forces, which are initially:

Accepted Answer

A) identical 
B) equal in magnitude but opposite in direction 
C) in the same direction and differing in magnitude by a factor of 1840 
D) in opposite directions and differing in magnitude by a factor of 1840 
E) equal in magnitude but perpendicular to each other 
A) identical 
B) equal in magnitude but opposite in direction 
C) in the same direction and differing in magnitude by a factor of 1840 
D) in opposite directions and differing in magnitude by a factor of 1840 
E) equal in magnitude but perpendicular to each other

Question 14

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long.A 0.7 T uniform magnetic field is in the plane of the triangle and is perpendicular to the hypotenuse.The resultant magnetic force on the two equal sides has a magnitude of:

Accepted Answer

A) 0 N 
B) 0.21 N 
C) 0.30 N 
D) 0.41 N 
E) 0.51 N 
A) 0 N 
B) 0.21 N 
C) 0.30 N 
D) 0.41 N 
E) 0.51 N

Question 15

An electron is moving north in a region where the magnetic field is south.The magnetic force exerted on the electron is:

Accepted Answer

A) zero 
B) up 
C) north 
D) south 
E) west 
A) zero 
B) up 
C) north 
D) south 
E) west

Question 16

A circular loop of wire with a radius of 20 cm lies in the xy plane and carries a current of 2 A, counterclockwise when viewed from a point on the positive z axis.Its magnetic dipole moment is:

Accepted Answer

A) 0.25 A.m2, in the positive z direction 
B) 0.25 A.m2, in the negative z direction 
C) 2.5 A.m2, in the positive z direction 
D) 2.5 A.m2, in the negative z direction 
E) 0.25 A.m2, in the xy plane 
A) 0.25 A.m2, in the positive z direction 
B) 0.25 A.m2, in the negative z direction 
C) 2.5 A.m2, in the positive z direction 
D) 2.5 A.m2, in the negative z direction 
E) 0.25 A.m2, in the xy plane

Question 17

You are facing a loop of wire which carries a clockwise current of 3.0 A and which surrounds an area of 5.8 x 10−2m2.The magnetic dipole moment of the loop is:

Accepted Answer

A) 3.0 A.m2, into the page 
B) 3.0 A.m2, out of the page 
C) 0.17 A.m2, into the page 
D) 0.17 A.m2, out of the page 
E) 0.17 A.m2, left to right 
A) 3.0 A.m2, into the page 
B) 3.0 A.m2, out of the page 
C) 0.17 A.m2, into the page 
D) 0.17 A.m2, out of the page 
E) 0.17 A.m2, left to right

Question 18

The magnetic force on a charged particle is in the direction of its velocity if:

Accepted Answer

A) it is moving in the direction of the field 
B) it is moving opposite to the direction of the field 
C) it is moving perpendicular to the field 
D) it is moving in some other direction 
E) never 
A) it is moving in the direction of the field 
B) it is moving opposite to the direction of the field 
C) it is moving perpendicular to the field 
D) it is moving in some other direction 
E) never

Question 19

For a loop of current-carrying wire in a uniform magnetic field the potential energy is a minimum if the magnetic dipole moment of the loop is:

Accepted Answer

A) in the same direction as the field 
B) in the direction opposite to that of the field 
C) perpendicular to the field 
D) at an angle of 45$\degree$ to the field 
E) none of the above 
A) in the same direction as the field 
B) in the direction opposite to that of the field 
C) perpendicular to the field 
D) at an angle of 45$\degree$ to the field 
E) none of the above

Question 20

The current is from left to right in the conductor shown.The magnetic field is into the page and point S is at a higher potential than point T.The charge carriers are:

Accepted Answer

A) positive 
B) negative 
C) neutral 
D) absent 
E) moving near the speed of light 
A) positive 
B) negative 
C) neutral 
D) absent 
E) moving near the speed of light

Exam 28: Magnetic Fields

A cyclotron operates with a given magnetic field and at a given frequency.If R denotes the radius of the final orbit, the final particle energy is proportional to:

The Hall effect can be used to calculate the charge-carrier number density in a conductor.If a conductor carrying a current of 2.0 A is 0.5 mm thick, and the Hall effect voltage is 4.5 µV when it is in a uniform magnetic field of 1.2 T, what is the density of charge carriers in the conductor?

The diagram shows a straight wire carrying a flow of electrons into the page.The wire is between the poles of a permanent magnet.The direction of the magnetic force exerted on the wire is:

J.J.Thomson's experiment, involving the motion of an electron beam in mutually perpendicular and fields, gave the value of:

The figure shows the motion of electrons in a wire which is near the N pole of a magnet.The wire will be pushed:

In the formula F ⃗=qv ⃗×B ⃗ :

A square loop of wire lies in the plane of the page and carries a current I as shown.There is a uniform magnetic field directed towards the top of the page, as indicated.The loop will tend to rotate:

An electron travels due north through a vacuum in a region of uniform magnetic field that is also directed due north.It will:

The diagram shows a straight wire carrying current i in a uniform magnetic field.The magnetic force on the wire is indicated by an arrow but the magnetic field is not shown.Of the following possibilities, the direction of the magnetic field is:

At any point the magnetic field lines are in the direction of:

A uniform magnetic field is directed into the page.A charged particle, moving in the plane of the page, follows a clockwise spiral of decreasing radius as shown.A reasonable explanation is:

A uniform magnetic field is in the positive z direction.A positively charged particle is moving in the positive x direction through the field.The net force on the particle can be made zero by applying an electric field in what direction?

An electron and a proton are both initially moving with the same speed and in the same direction at 90˚ to the same uniform magnetic field.They experience magnetic forces, which are initially:

A loop of wire carrying a current of 2.0 A is in the shape of a right triangle with two equal sides, each 15 cm long.A 0.7 T uniform magnetic field is in the plane of the triangle and is perpendicular to the hypotenuse.The resultant magnetic force on the two equal sides has a magnitude of:

An electron is moving north in a region where the magnetic field is south.The magnetic force exerted on the electron is:

A circular loop of wire with a radius of 20 cm lies in the xy plane and carries a current of 2 A, counterclockwise when viewed from a point on the positive z axis.Its magnetic dipole moment is:

You are facing a loop of wire which carries a clockwise current of 3.0 A and which surrounds an area of 5.8 x 10−2m2.The magnetic dipole moment of the loop is:

The magnetic force on a charged particle is in the direction of its velocity if:

For a loop of current-carrying wire in a uniform magnetic field the potential energy is a minimum if the magnetic dipole moment of the loop is:

The current is from left to right in the conductor shown.The magnetic field is into the page and point S is at a higher potential than point T.The charge carriers are:

Measurement

Motion Along a Straight Line

Vector

Motion in Two and Three Dimensions

Force and Motion I

Force and Motion II

Kinetic Energy and Work

Potential Energy and Conservation of Energy

Center of Mass and Linear Momentum

Rotation

Rolling, Torque, and Angular Momentum

Equilibrium and Elasticity

Gravitation

Fluids

Oscillations

Waves I

Waves II

Temperature, Heat, and the First Law of Thermodynamics

The Kinetic Theory of Gases

Entropy and the Second Law of Thermodynamics

Electric Charge

Electric Fields

Gauss Law

Electric Potential

Capacitance

Current and Resistance

Circuits

Magnetic Fields Due to Currents

Induction and Inductance

Electromagnetic Oscillations and Alternating Current

Maxwells Equations; Magnetism of Matter

Electromagnetic Waves

Images

Interference

Diffraction

Relativity

Photons and Matter Waves

More About Matter Waves

All About Atoms

Conduction of Electricity in Solids

Nuclear Physics

Energy From the Nucleus

Quarks, Leptons, and the Big Bang

Filters

You are facing a loop of wire which carries a clockwise current of 3.0 A and which surrounds an area of 5.8 x 10⁻²m².The magnetic dipole moment of the loop is: